Electric discharge tube for highfrequency amplification



June 25, 1957 G. DIEMER ETAL ELECTRIC DISCHARGE TUBE FOR HIGH-FREQUENCY AMPLIFICATION Filed May 13. 1953 2 Shets-Sheet l INVENTORS Gesirws Diemer Komelis Sun' r Km! h Wlgbolf .dens

Abraham e erfmdaatwilhelms Y I Jens AEEN June 25, 1957 G. DIEMER HAL 2,797,266

ELECTRIQDISCHARGE TUBE FOR HIGH-FREQUENCY AMPL IIFICATION Filed May 15. 1953 2 Sheets-Sheet 2 BY W AeEN

United States Patent 6 ice ELECTRICDISCHARGE BE FO HIGH- rnnonnncr AMPLIFICATION Gesinns Diemer, Korneli's-Swier Knol Jan Wigbolt Edens and Abraham Geertrudas Wilhelmus Uitjens, Eindhaven, Netherlands, assignors; by' mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application May 1-3, 1953, Serial-No. 354,846

4 (Jlaims. (Cl. 179-411) This invention relates to an electric discharge tube for amplifying high frequencies (30 to. 1000 mc./s.) and, more particularly, to an electric discharge tube comprising a pair of distinct electrode systems.

A popular circuit arrangement for amplifying electrical signals in the U. H. F. or V. H. F. portions of the electromagnetic spectrum (30 to 1000 mc./s.)., more particularly, for the reception of television signals,-is known as a cascode arrangement. In this arrangement, a pair of tr-iode systems are employed, the first system of which is operated as a grounded cathode, and the second system of which is operated as a grounded grid. The chief advantages of this arrangement is that the grounded cathode triode, which is usually directly coupled to the antenna, renders the antenna reflection-free even if the amplification of the system is varied.- Moreover, the provision of the grounded grid tri'ode serves to isolate the antenna from the local oscillator and prevents the production of noise or input impedance reduction of the grounded cathode triode.

The advantageous properties of the foregoing arrangement can be further enhanced by minimizing the input damping, the Variation in input capacitance, and the inductance of the conductors of the system.

Theprincipal object of the invention is to provide an electric discharge tube comprising apair of elect-rode systems designed particularly for operation in a cascode arrangement.

A further object of the inventionis to provide an electric discharge tube comprising a pair of triode systems disposed within a single envelope for operation in a cascode arrangement in which the. input damping, the variation of input capacitance, and the inductance of the conductors is minimized.

These and further objects of the invention will be best understood from the following description.

According to the invention, an electric discharge device for amplifying frequencies of the order of 30 to 1000 mc./s. comprises a pair of electrode systems disposed within a single envelope. The cathode of one of the electrode systems is capacitatively coupled to the control grid of the other system by being connected directly to a conductiv'e, e. g., metal, screen disposed within the envelope (and which forms a capacitor together with a second conductive, e. g., metal, screen which is connected directly to the control grid of the other system. The grid of the other system is thus grounded by being connected to the grounded cathode of the first system by means of the capacitor formed by the two screens; consequently, low input damping and excellent screening are obtained. The tube is further designed to be operated such that the amplification factor of the two systems is less than 40 and so that the cathodes of each of the systems have a small surface, e. g., less than 15 square mm., and operate under high load, i. e., the continuouscathode current Ik is more than of saturation plate current Is.

In accordance with further features of the invention,

2,797,266 Patented June 25, 1957 theicathode. of the first system is connected to the first conductive screen by one or more connecting conductors having a length of less than 3' mrns., and, moreover, this cathode. and screen are each provided with one separate connection to. an individual contact pin of the tube, the positions of these pins and the lengths of the connecting conductors being such that the relative inductance of the two supply conductors less than 3x10" henrys.

Such a system in which separate cathode leads are provided has a low input impedance, provided that the anode current is prevented from inducing current into the input circuit. In the cascode arrangement, the anode current of the first system flows back through the grid of the second system and thus prevents the induction of current in the input circuit.

The stay rods for the grid of the second system are secured directly to the associated conductive screen and the. other ends of these stay rods may also be secured to the screen to obtain further a reduction of the input impedance.

By employing a tube according to the invention, very satisfactory results may be obtained in the frequency range of 30 to I000 mc./s. without the necessity of employing expensive tubes having sealed-in discs, e. g. lighthouse tubes.

' The invention will now be described with reference to the accompanying d-rawing in which:

Fig. 1 shows a cascode circuit-arrangement;

Fig. 2 shows diagrammatically an electric discharge tube according to the invention;

Figs. 3a and 3b are sectional views of only the electrode systems in the tube shown inFig. 2;

Fig. 4. shows the connections of the electrodes to the contact pins of the tube shown in Fig. 2;

Fig. 5 is a. modified circuit diagram of the cascode arrangement shown in. Fig. 1;

Fig. 6. shows another form of the connections of the tube pins to the various electrodes.

In order to obtain optimum operation of the cascode circuit-arrangement shown in Fig. 1, the following requirements must be fulfilled by the discharge tube. The first electrode system. must cause little input damping so that satisfactory amplification is obtained, and so that matching of the aerial system is satisfactorily maintained even if the amplification is varied. This requires that the cathode inductance must be low and the transit time of the electrons must be short, which can best be fuhilled by a low cathode-grid capacity and short cathode supplyconductors. Moreover, in a triode, which is required for this situation toavoid a high noise figure, the distances between the cathode and the grid and the anode must be minimized.

A high conductance of the tube is also desirable; however, since the dimensions of the electrodes must be small inorder to reduce the capacities, the conductance must be obtained by using a greater current density. The continuous current to be supplied by the cathode must therefore be a considerably greater part of the saturation current i. e., at least greater than 10%, than is obtainable with normal oxide cathodes. This is achieved by employing a special dispenser cathode of the type described in U. S. Patent 2,547,728.

The use of a great current density implies that the elfective, static potential in the control-grid plane must be high. This has the advantage that the transit time and hence the noise are reduced. But in order to obtain the high potential in the control-grid plane for normal anode voltages, it is necessary to choose the statistic am plification factor to be comparatively low, preferably less than 40.

All these requirements are fulfilled by a tube as shown in Fig. 2, which comprises two substantially identical triode systems, which are separated from one another by a pair of conductive screens which form the interconnecting capacitor C (Fig. l) of, for example, 100 to 200 #[Lf- In addition, the impedances of the supply conductors of the cathode of the first system and of the grid of the second system are kept extremely low.

Referring to Fig. 2, of which the parts corresponding to that of Fig. l have the same reference numerals, an electric discharge tube in accordance with the invention comprises an envelope including a tube bottom in which nine supply pins 2 are sealed to form a circle for ten pins. The cathode 3 of the first triode system is connected through short conductors (shorter than 3 mms.) to screens 7 and 9, which are interconnected by a screen 8. The cathode 3 is, moreover, connected to a pin k1-1 and through the screen 7 also to a pin k1-2. Consequently, the impedance of the supply conductors to this cathode is associated with various circuits, as is already evident from Fig. l. The relative inductance of these cathode leads must preferably be lower than 3X10 henrys. The control-grid 4 is arranged as closely as possible about the cathode 3. The distance is determined by the mechanical possibilities and the cost of manufacturing. The distance between the cathode and the grid is, in general, about 100 microns or smaller and the distance between this grid and the anode is about 300 microns or smaller.

Since the arrangement of a grid at a small distance from another electrode is carried out, from a technical point of view, in an easier fashion than the identical arrangement of a plate-shaped anode to an electrode, an electrode 5 in the form of a grid is provided to surround the grid 4; however, this grid 5 is connected directly to the anode 6, as is evident from Figs. 3a and 3b. In this case, the distance between the first grid and the second grid may be about 150 to 250 microns.

The conductive screen 9, besides serving to screen the getter space, also is employed, together with the screen 8,

to form the capacitor C (Fig. 1) together with conductive screens 10 and 11. These screens are separated from one another by insulating, e. g., mica, plates 12 and 13. Additional mica plates are provided for centering and securing the electrode systems in the tube in a conventional manner. As is evident from Fig. 4, the systems are shifted in position in the envelope in accordance with the positions of the pins. The anodes 6 and 17 are formed by narrow plates, arranged parallel to the cathodes and secured by short tags to the sealed-in pins a1 and a2 respectively. This improves the cooling of the anode. Each anode plate preferably has a smaller surface than the active surface of the associated cathode.

In the second triode system, the cathode 14 is connected to a supply conductor, and the grid 15 is supported by stay rods which are connected directly to the screen 10. The screen 18 is connected to the lower ends of the stay rods of the grid 15 and to the connecting pin In this case, the inductance of the conductors is arrangement as shown in Figs. 5 and 6. In Fig. 5, the anode of the first system is connected directly to the cathode of the second system. If desired, an inductor may be included in this connection in order to neutralize the effect of the grid-cathode capacity of the second system, for example, for the highest frequencies at which the arrangement is employed. This connection may be housed completely inside the tube, including the resistor between the cathode and the grid of the second system. The filament wires of the two cathodes may then be connected to separate contact pins, which is of advantage with a view of decoupling the filament wires. The connection of the electrodes to the pins may then be carried out, for example, as shown in Fig. 6.

In the circuit-arrangement shown in Fig. l, the two systems are connected in series for direct current, which permits a uniform control of the amplification. However, as an alternative, the systems may be fed in parallel.

In Figs. 1 to 6, wherever reference letters with subscripts are shown, the subscript 1 refers to the first triode system whereas the subscript 2 refers to the second triode system. The letters 1, k, g and a refer, respectively, to the filament, cathode, control grid and anode.

It is obvious that the conductive screens may be shaped in another form within the scope of the invention.

While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electric discharge tube comprising an envelope, a pair of distinct triode electrode systems within said envelope, each of said systems including a cathode, an anode, and a control grid, a capacitor within said envelope between said electrode systems and comprising a pair of conductive screens separated by a solid dielectric, said screens substantially completely electrically shielding and isolating said systems from each other, a connection from the cathode of only one of said systems to one of said kept extremely low. The screen 19 is preferably arranged at right angles to the plane of the stay rods of the second system, so that the anode supply conductor may be very short and be kept completely separated from the cathode supply conductor.

The choice of the connections to the various contact pins must also be carried out carefully. Since the filament current pins are preferably arranged side by side for technical reasons, an arrangement as shown in Fig. 4 may be chosen. Provision must be made that the pins K1-1 and Kl-Z are at least spaced apart by a distance equal to two distances between the pins, measured across the pin circle. This also applies to 112 and g1, and k2 and a2 must be arranged each on one side of the screen 9.

r The screens may be prolonged in a simple manner outside the tube.

The tube of the invention can be employed in a further conductive screens, and a connection from the control grid of the other of said systems to the other of said conductive screens.

v 2. An electric discharge tube comprising an envelope, a pair of distinct triode electrode systems within said envelope, each of said systems including a cathode, a con- .trol grid and an anode, a pair of U-shaped metal screens arranged back-to-back and each extending around three sides of one of said systems, respectively, a solid dielectric insulating said screens from each other, and the -base sides of said U-shaped screens forming with said dielectric a capacitor, a ,direct connection from the cath- 3 ode of only one of said systems to one of said screens, a direct connection from the grid of the other of said sysitems to the other of said screens, a plurality of contact,

pins extending through said envelope for making external connections to the electrodes of said systems, a conductor 'having a relative inductance of less than 3X10 henrys connecting said cathode of said one system to one of said :contact pins, and another conductor having relative inductance of less than 3 1O' henrys connecting said one screen to another of said contact pins.

3. An electric discharge tube as claimed in claim 2 in L which the cathode of said one of said systems is in the form of a tube extending between the open arms of one said U-shaped screens and is connected at opposite ends through separate conductors to said open arms and through another individual conductor to a separate contact pin of the tube to reduce the inductance in series with said cathode.

4. A circuit arrangement for amplifying frequencies of 30 to 1000 mc./s.; comprising an electric discharge tube, said tube comprising an'envelope,'a pair of triode electrode systems disposed within said envelope each including a cathode, a grid and an anode, said cathodes having a smaller active surface than 15 mm, a capacitor disposed within said envelope, said capacitor comprising a pair of metal screens disposed between said systems, the cathode of one of said systems being directly connected to one of said screens, the grid of the other of said systems being directly connected to the other of said screens; means for grounding the cathode of said one system; means for applying potentials to the anodes of said systems at which the normal operating current through said systems is greater than 10% of saturation current of said systems; said circuit being operated so that the amplification thereofis less than 40.

6 References Cited in the file of this patent UNITED STATES PATENTS 1,867,577 Loewe July 19, 1932 2,021,891 Hollmann Nov. 26, 1935 2,077,326 Kapteyn Apr. 13, 1937 2,092,769 Maurogenis Sept. 14, 1937 2,144,784 Ardenne Jan. 24, 1939 2,150,800 Jordan Mar. 14, 1939 2,232,220 Feindel Feb. 18, 1941 2,431,740 Eitel Dec. 2, 1947 2,455,373 Lester Dec. 7, 1948 2,448,070 Sustein Aug. 3, 1949 2,534,077 Stevens Dec. 12, 1950 

